Just looking for a few opinions. We have a Windows Server 2003 64-bit with 4GB RAM running Exchange 2007, configured as an "all in one box" Exchange solution. We have about 120-140 users/mailboxes. Generally it performs quite well. It is currently configured to forward all outbound mail via a "smart host" located at our ISP. The problem: our ISPs SMTP server occasionally (and increasingly) is named in various RBL lists, meaning that our outbound mail bounces until the RBL entry is removed. Possible solution: we could drop the "smart host" and send out our mail directly to the outside world. Pros and Cons: on the plus side, our ISP being RBL'd won't affect us, but on the down side there would be additional load on our server, plus if we ourselves get RBL'd its then down to me to fix it Considering the possible extra load which sending mail directly would place on the server, how would y'all handle this? Should I go direct, or stick to the smart host approach? Any clues on how much additional load I might see on my server?

The ISP gets on RBLs? Thats not good. Or is it SPAMCOP or some other zealot RBL? Anyway, why not build your own smarthost? Any SMTP gateway will do. You could even use it to handle inbound mail as well then route to the Exchange Server. A hardened IIS server running SMTP is simple to install and maintain. Im not a big fan of sending or receiving mail from the internet directly to and from the Exchange server. Large outbound queues could build on it and it could affect server perfomance. Oh, and make sure you do recipient filtering against users in AD. That will cut down tremendously on the amount of mail the server actually has to handle and will go along way to keeping you off RBLs.

Thanks Andy, Yeah, I must confess I am none too impressed with the ISP RBL situation either. I have asked them whether they know why they are being RBL'd and which of their customers is responsible ... no reply yet. I like your idea of building our own smart host. We could put it in our DMZ I suppose and use the IIS SMTP service to do the work. I'll have a think about that and make a recommendation to the boss in due course. Your input much appreciated!